The development of a reliable, general purpose interface system for optical networks presents the most critical problem to be solved before many diverse fiber-optic sensors can be integrated into complex systems, for example, aircraft systems. Such an interface system must provide optical power, multiplexing, read-out, and signal processing functions for a wide variety of sensors.
A particularly promising fiber-optic sensor/network interface system is one based upon the use of wavelength division multiplexing (WDM). However, the development of a WDM system depends upon the development of a suitably broadband optical source. For many applications, for example in aircraft, the optical source must retain its broadband characteristics over a significant temperature range. The long life, small size, and high coupling efficiency of edge-emitting LEDs are ideal characteristics for the broadband source of a WDM-based sensor interface system. Unfortunately, the spectral widths of commercially available edge-emitting LEDs are much too narrow to meet the requirements of a WDM system. In particular, typical edge-emitting LEDs yield a full spectral width at half maximum (FWHM) of no more than about 30 nanometers. In comparison, the spectral width requirement for a WDM broadband source is on the order of 150 nanometers.